<!doctype html>
<meta charset="utf-8">
<title>Issue 18631: Assertion failure when double-adding the UA sheets to the page</title>
<style>
* { display: none }
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
// Trigger two forced reflows.
test(function() {
  document.documentElement.offsetTop;
  document.documentElement.offsetTop;
  assert_true(true, "Didn't assert");
}, "Passes if it doesn't assert");
</script>
